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The Circle of Life! Brain Busters for Your Classroom

The Circle of Life! Brain Busters for Your Classroom. Presented by: Rebecca Jackson Elyssa Adams. Concentric Circles. What if we inscribed a circle into a square . Now, inscribe that square into a larger circle. Which Area Is Bigger?. The purple ring? The yellow circle?

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The Circle of Life! Brain Busters for Your Classroom

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  1. The Circle of Life!Brain Busters for Your Classroom Presented by: Rebecca Jackson Elyssa Adams

  2. Concentric Circles • What if we inscribed a circle into a square. • Now, inscribe that square into a larger circle.

  3. Which Area Is Bigger? • The purple ring? • The yellow circle? • Are they equal? • Not enough information to answer?

  4. Concentric Circles • Let’s bring back the square. • We can find the radius of the yellow circle. • Using Right Triangle Trig, we can then find the radius of the purple circle. • Since we know both the radii of the yellow and purple circles, we can find the area of each. r

  5. The Results… • Do you want to change your answer now? Does anyone know what the answer is? • By subtracting the yellow area from the purple area, we come to find that… • Their areas are EQUAL! r

  6. The Benefits Of This Problem: • Real-Life Applications: • Tires and Wheels • Donut vs. Tim-bit • Architecture • Topics Covered: • Properties of Circles • Area • Diameter • Radius • Right Triangle Trig

  7. If a penny has a diameter of .75 inches and the circle has a diameter of 1.5 inches, how far will the penny have traveled after one revolution? Taking a Lincoln for a spin!

  8. Let’s Try It! • Everyone please take a penny and a circle. • Try rotating the penny around the circle once (without it sliding), keeping track of how many revolutions you get. • Did the person next to you get the same number?

  9. The Mathematics Behind It • Similarity of Circles • We can set up a proportionof circumferences and radii • Does anyone have an answer yet? • 1 revolution = =.5 • After one revolution, the penny will have traveled half the circumference of the circle. • Is it always .5? • No! Why? This is just because the penny had half the radius of the larger circle.

  10. Crafty Crescents • Given this figure, which as more area? • The pink? • The yellow? • Or are they the same?

  11. Crafty Crescents • If we let be the base and height of the triangle. • We can also find the area of the larger blue circle. • will give us the area of the blue areas adjacent to the triangle. • So now what?

  12. Crafty Crescents • Now we need to subtract the area of the blue regions from the pink semicircles. • Finding the area of the pink semicircle: • Subtracting the areas to get the pink crescents. • Does anyone notice anything? Do you have an answer? • The answer is… • The areas are the same!

  13. The Benefits Of This Problem: • Topics Covered: • Properties of Circles • Area • Radius • Diameter • Inscribed Angles • Triangle Area • Semi-circles • Right Triangle Trig • Problem Solving Skills • Real-Life Applications: • Painting • Architecture • Sewing

  14. Why These Are Good Problems • Twist on classic geometry problems • Help students utilize basic topics and apply them in different, creative ways • Allow students to think “outside of the circle”

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